Ferulic acid is an important component of plant material, forming crosslinks between polysaccharide chains and between polysaccharides and lignin, thus providing structural rigidity to cell walls. Ferulic acid is a cinnamic acid with the chemical name (3-methoxy-4-hydroxy)-3-phenyl-2-propenoic acid, or 3-methoxy-4-hydroxy-cinnamic acid. In the plant cell wall, ferulic acid is bonded via an ester linkage to hydroxyls on sugars, usually arabinose moieties in arabinoxylans or galactose residues in pectins. Ferulic acid dimers and trimers formed by linkages between the phenolic groups provide covalent crosslinks among cellulose, arabinoxylan, xyloglucan, pectin, lignin, as well as protein. The amount of dimers account for 0.14% and 2.5% w/w of the enzyme digest of sugar-beet pulp and corn bran, respectively, suggesting a high degree of crosslinking in the bran cell wall of corn. It has been calculated that each heteroxylan macromolecule contains ˜75 esterified ferulic acid groups and ˜30 diferulic bridges. These crosslinks limit carbohydrate bioavailability, resulting in lower conversion of the plant material into useful products or nutrients. To overcome this limitation, the ester bonds are hydrolyzed by feruloyl esterases, which are produced by numerous microorganisms that utilize complex plant material as nutrients. Feruloly esterases (FAE, E.C. 3.1.1.73) (ferulic acid esterases, cinnamoyl esterases, cinnamic acid hydrolases, p-coumaroyl esterases, hydroxycinnamoyl esterases, etc.) belong to a subclass of carboxylic esterases (E.C. 3.1.1). The enzyme cleaves ester bonds between hydroxycinnamic acids esterified to arabinoxylans and certain pectins present in plant cell walls.
Feruloly esterase forms a part of the enzyme complexes that are elaborated by fungi or bacteria that metabolize plant materials. FAE plays a key role in enhancing the accessibility of other biomass-degrading enzymes, and subsequent hydrolysis of plant fibers by removing the ferulic acid side chains and crosslinks. This enzyme reaction may well be an important controlling factor for increasing the extent of degradation of lignocellulosic biomass for bioenergy conversion, and pulp and paper manufacture. In biomass degradation, FAE is an integral part of an enzyme system that acts collectively and synergistically with a variety of other cellulolytic and xylanolytic enzymes to enhance biomass degradation. This in turn increases the yield of hexose and pentose sugars in the bioconversion as feedstock for yeast fermentation to biofuel or other value-added chemicals. The enzyme also aids in solubilizing lignin-polysaccharide complexes in paper pulp processing. The enzyme together with a number of glycanases and oxidases, have been implicated in the improvement of bread-making quality and related cereal processing. The importance of FAE also relates to the enzyme product, ferulic acid and feruloylated oligosaccharides, which have potential applications for food and medicinal uses. Ferulic acid and its derivatives are strong antioxidants, and have gel-forming properties. The biotransformation of ferulic acid to vanillin has been extensively investigated. The antioxidative and gelling effects have been utilized to form potential protective agents against photooxidative skin damage and for wound management.
The use of feruloyl esterases for biomass degradation and conversion has been severely hampered by the fact that there are very few known existing gene sequences and enzymes, due to the lack of workable, effective, high-throughput method for direct gene discovery of this group of enzymes. An expanded diverse pool of feruloyl esterase genes/enzymes would enable fine control over processing of complex and variable biomass materials. The immediate impact of the development is to increase the extent of degradation of lignocellulosic biomass for bioenergy conversion as well as for food and medicinal uses.
Technologies enabling rapid discovery of new genes, new enzymes, new reactions and processes are key to continuous growth in the use of biocatalytic processes in many industries. Increasing the number of enzymatic candidates feasible for increasing the commercial viability of biomass conversion is key for the fuel ethanol industry and would equally benefit other industries, such as pharmaceuticals, diagnostics, cosmetic, food and beverages and other sectors employing biocatalysis as a technology platform. A method enabling rapid discovery and isolation of more efficient biocatalytic genes is therefore desired.